There seems to have been a peak that may now have passed. The recent mite-fall figures are: 5th June 0; 6th June 0; 7th June 2; 9th June 1; 12th June 9; 14th June, 11.50 am 30 + 26 at 6.30pm; 16th June 23; 18th June 8.
I used my dissecting microscope (which doesn’t come out of its box every year!) to look at the mites that I collected on 14th June. 2 had cracks at the periphery of the carapace. Very many of them had limbs that appeared still to be immature and not free to move. A couple had limbs missing. None looked perfectly formed and raring to go.
Today I had a quick look at those I had collected the day before yesterday, ie, 16th June. One of them was alive and well and scampering about! Most of the others looked immature though. There is much less in the way of pupal antennae than there was.
My guess as to what has happened is that the cast came with a load of mites and a virgin queen. She took some time to get mated and come into lay, but when she did, nearly all the mites dived into the cells soon before the larvae were sealed. Where there were more than one mite per cell they may have fed too heavily on the pupae and killed/wounded them and the resulting aroma was detected by the worker bees which dug them out, hence the pupal bits falling through the mesh. I assume the other bits either were larger and so couldn’t fall through or else were eaten or chucked out of the entrance.
The sharp peak of mitefall must be from those cells where the bees managed successfully to complete their pupal stage despite being heavily laden. Being workers, their time of development within the sealed cell is 3 days less than it would be if they were drones.
It might be possible for somebody cleverer than I am at figures to work out how many mites there are now within the hive.